Who Would Have Thought It? Which Would You Bet Are Easier to Cultivate, Abundant Bacterial Species or Rare Ones?

Surprises are the stuff of science, but some discoveries are more surprising than others. We are starting a new column, its aim being to highlight findings that, in our view, lie outside the norm for being markedly unexpected and unforeseen. We plan to post notices of such items periodically. You are invited to submit your own choices.

Although only a small fraction of the bacteria on Earth can be cultivated, the existence of many others has been inferred from the presence of their DNA in environmental samples. This two-fold approach sounds innocuous enough, but it has occasionally resulted in acrimonious controversies. This is puzzling because even a moment’s reflection should lead one to conclude that these strategies are complementary and that both are needed. But putting that aside, consider that bacterial species are far from uniformly abundant in the environment. Some are found in large numbers, others are exceedingly rare. Now, which do you think would be easier to culture, the abundant ones or the rare ones? If you bet on the abundant ones—surprise, surprise—you’d be wrong, even if your answer feels intuitively obvious.